1. Field of the Invention
The invention relates to a turbine blisk. In particular it concerns the manner in which a turbine blisk may be manufactured.
2. Description of Related Art
The term blisk is a contraction of the two words “bladed disk” and is used in the field of gas turbine engines to refer to a unified assembly of a turbine disk together with a circumferential array of turbine blades. It may be used in the case either where the whole assembly has been machined from a single piece of metal or where the supporting disc and the blades have been irreversibly joined, for example by welding. “Single piece of metal” shall be taken for present purposes to include a metal article, such as the turbine disc, made from metal powder, which has been joined into a whole by a hot isostatic bonding process.
The use of powder metallurgy for manufacturing blisks for use in gas turbines is well known in the art and has been described in numerous publications. None of the publications has discussed solutions to the problems associated with heating of the disc head as a result of exposure to the main hot gas flow. No blisk so manufactured has incorporated cooling into the turbine aerofoil. So it has been accepted, until now, that the use of Blisks is restricted to compressors because turbine sections are too hot.
Current manufacturing processes and designs do not allow for the blades or the rim of the rotor disc to be cooled. Current designs use the platforms of the rotor blades to form the outer annulus of the rotor disc. Therefore, in practice, the engine main hot gas heats the platforms and consequently the rim of the disc. This results in lower mechanical properties and limited life of the part due to creep failure. In the absence of provisions to cool the blades internally, the use of the design and the operating temperature of the rotor blades is further limited. This imposes a maximum limit on the operating temperature of blisks so designed and made, and particularly precludes the use of this type of blisk in turbines. An objective of the present invention is to overcome these drawbacks. Further advantages will be apparent in the following description of the invention.